Any community that talks about this stuff, and doesn't even use proper non-ambiguous terms, is just doomed to have flamewars.
"Atheist" and "agnostic", unspecified, are virtually useless in any conversation *about* religion and stances towards theism.
Using those terms unspecified, and then saying "ha ha ha no you shall not define it as including both atheism and agnosticism" is ridiculous.
So as a short list:
1. Theism - belief in at least one god
- more variants than I want to get in to in a post about atheism...
2. Non-theism, aka weak atheism - no belief in a god. Includes the (mostly) mutually exclusive terms:
2.1 strong atheism - belief there *are* no gods
2.1.1 uncertain strong atheism - belief, but not knowledge, that there are no gods
2.2 strong agnosticism - belief that the existence of gods is definitely unknowable
2.3 weak agnosticism - belief that the existence of gods is currently *unknown*, but might be knowable with the right data
- both versions of agnosticism are compatible with theistic and strong-atheistic variants, if you're willing to do the twisty method of saying that 'knowledge' and 'belief' are separate, i.e. you don't *know* there is a god, and indeed you think you can't have any evidence for one, but you believe in one anyway... that's theistic (weak/strong) agnosticism.
... compatible with:
2.4 non-theistic religion - religion that lacks a deity, e.g. Taoism, Buddhism, "secular Christianity" (!), et al.
2.5 antitheism - belief that the belief in a god, is a Bad Thing
2.6 implicit vs explicit ~ism - whether someone's actually thought about it
That's the basic categories at least - the ones that come up most often. I find it really irritating when people discuss this, and then get in a fight over wtf the definition of 'atheist' is, and then resort to bullshit etymological "arguments" to "prove" that their definition is right. (?!!) Hint: in polite formal debate, you have to first agree on all definitions and evidence, THEN discuss what conclusions to draw. Otherwise you just end up it pointless headbutting.
FWIW it's my belief that weak agnosticism is the only rigorously defensible position, absent either data I don't have (e.g. direct communication from a god?) or the willingness to make moves I consider to be just really sketchy (and unnecessary), like a difference between knowledge and belief. YouTube has tons of videos against theism, some of which are pretty good (I am partial to those by 2LegHumanist and and blueadept111); I have a series attacking strong atheism (in favor of weak agnosticism).
I also think it's sad that religion seems to have a chokehold on 'sacred' experiences. There are many conversion stories I've read that basically start "I saw something amazingly beautiful" or "I had an incredible bit of luck and my life changed for the better" and end "... and therefore I believe in Jesus". WHY?!?! The only answer I can think of is because they have no other framework in which to parse that sort of experience. Which is, to me, sad, because then the religious crap takes over and dilutes the sacredness part. :-/
Anywho: Plz to not be using unqualified terms 'atheist' and 'agnostic'. Extra plz to not be arguing over definitions of such ambiguous terms. Kthxbye!